Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $172.93   5.576%   $182.5726   $182.57   $182.55   $182.60  
  Purchase #2 $153.70   13.633%   $174.6539   $174.65   $174.65   $174.70  
  Purchase #3 $235.91   9.262%   $257.76   $257.76   $257.75   $257.80  
  Purchase #4 $31.27   13.267%   $35.4186   $35.42   $35.40   $35.40  
  Purchase #5 $224.88   5.261%   $236.7109   $236.71   $236.70   $236.70  
  Purchase #6 $177.70   3.627%   $184.1452   $184.15   $184.15   $184.10  
  Purchase #7 $150.72   3.520%   $156.0253   $156.03   $156.05   $156.00  
  7 purchase totals = $1,147.11       $1,227.2865   $1,227.29   $1,227.25   $1,227.30